Lacking an understanding of the earth's massive and complex

Lacking an understanding of the earth's massive and complex ecosystem, many people tend to overestimate the importance of organisms, such as human beings, that are at or near the top of the food chain, and underestimate that of micro-organisms, such as plankton, that dwells near the bottom of the food chain .

A) organisms, such as human beings, that are at or near the top of the food chain, and underestimate that of micro-organisms, such as plankton, that dwells near the bottom of the food chain.
B) organisms, such as human beings, that are at or near the top of the food chain, and underestimate it when micro-organisms, such as plankton, dwell near the bottom of the food chain.
C) organisms, such as human beings, that are at or near the top of the food chain, and underestimate it for micro-organisms, such as plankton, who dwell near the bottom of the food chain.
D) organisms at or near the top of the food chain, such as human beings, and underestimate that of micro-organisms near the bottom of the food chain, such as plankton
E) organisms at or near the top of the food chain, such as human beings, and underestimate it when considering micro-organisms near the bottom of the food chain, such as plankton


My answer is D


B --> underestimate "it" -- unclear what it refers to, clearly we need to refer to "importance"
E -->Similar reason as in B